This invention relates to a method and apparatus for electrically testing a multi-core cable, and particularly relates to a method and apparatus for electrically testing whether there is a defective contact or dielectric breakdown between adjacent cores of the multi-core cable which has an enormous number of insulated cores and serves as a communication cable and the like.
Generally, as for such a multi-core cable, whether adjacent cores are in defective contact or dielectrically broken clown on application of a voltage must be inspected and tested, order to guarantee the quality of the cable, in the intermediate or final state of cable production. There have been conventionally known various kinds of electric testing methods and apparatus For the above inspection and test.
For example, Japanese Patent Application Publication Gazette No. 57-51067 discloses a method for electrically testing a multi-core cable, in which the following steps are carried out. That is, a group of plural cores in a multi-core cable are first collectively conducted at the near ends thereof while isolated From one another at the far ends thereof. In this state, the cores are picked up one by one out of the group of cores at the near ends and are transported one by one, and then the transported core is electrically separated from the collectively conducted part located at the near ends of the group off cores. Subsequently, while the core is transported, the core is made contact with an electrode so as to be electrically charged and then contact judgment is made about whether or not an insulation characteristic between the picked-up core and other cores is normal based on whether or not an electric conduction characteristic of a charging current between the charged core and the group of cores at the near ends is a specific electric conduction characteristic of a charging current. Further, while the core is transported, the electric charge applied to the core is discharged. Next, the discharged core is electrically charged again and then confirmation is made about whether or not the above contact judgment is correct based on whether or not electric conduction characteristics of discharging and charging currents between the picked-up core and the group of cores at the near ends are specific electric conduction characteristics of discharging and charging currents.
In this case, the picking-up of a core is made by engaging a single core with a groove provided on the outer periphery of a rotary disc. The transportation of the picked-up core is made by rotating the rotary disc with the single core engaged with the groove. Then, during the rotating operation of the rotary disc, there are performed the contact between the picked-up core and the electrode, the judgment based on the electric charging, and the confirmation of the judgment based on the discharging and the subsequent electric charging. In short, in the above electric testing method, inspection and test are performed in such a manner as to charge and discharge the core within the time period when the core during rotary movement is kept in contact with the electrode.
As mentioned above, in the above conventional electric testing method, the picked-up core is charged and discharged during its movement toward the electrode. However, if the electrode is worn, a contact of the core with the electrode may be reduced in time or lost so that a stable contact of the core with the electrode cannot be secured. In such a case, a predetermined amount of charging current cannot be applied to the core or no charging current cannot be applied thereto, so that the contact judgment may not be correctly made thereby resulting in a misjudgment or the judgment itself may be impossible. In particular, since the picked-up core comes into contact with the electrode while moved by the rotation of the rotary disc, a shock at the contact of the core with the electrode while moved invites vibration of the electrode, so that a continuous contact of the core with the electrode may not be secured. Such a disadvantage often generates in the case that the electrode is forced by a resilient member such as a spring.
Further, if insulation cover layers each of which covers a large number of cores forming the multi-core cable are different in thickness from one another or if the core is decentered in the insulation cover layer, a duration of contact between the core conductor and the electrode varies from core to core. In such a case, it may be impossible for some cores to be sufficiently electrically charged through the electrode.
In view off the forgoing problems, this invention has been made. An object of this invention is to effectively prevent an unstable inspection owing to a worn electrode thereby increasing the stability and accuracy of the inspection.